I was born in Zadar, on the Croatian Adriatic coast. Compared to fruit available there, a lot of fruit in Ontario is terrible. It's kind of like listening to a 32kbps MP3 or PC speaker playback instead of a CD. Often, major components of taste are barely noticeable or missing. Some fruit can even be tasteless or a bad mix of unripe and rotten. Sometimes, it's possible to obtain good fruit by buying it from roadside stands and picking your own. Here I will list some of what I discovered.
In spring, some very nice imported strawberries may be found in supermarkets. Many Ontario strawberries are less sweet and tasty and/or more acidic. However, I have repeatedly found good strawberries at Schoger Orchards (432 County Rd. 34, between Essex and Cottam, 519-839-4675) and Raymont's Berries. Usually, local strawberries are only available in June, but at Raymont's Berries, they're available from around mid May to Thanksgiving or beyond. It seems pick your own is only available in late spring, but good prices on already picked flats and large baskets are available year round.
Note that strawberries don't need to be fully dark red. In fact, the really dark ones are overripe, less tasty, and more vulnerable to spoilage. Those with a bit of lighter colour on them can still be ripe, sweet and tasty. Also, note that while larger size makes picking easier, it doesn't guarantee good taste.
Ontario cherries are usually less sweet, less tasty and more acidic. In almost all cases, the imported cherries in the supermarket are better. So far, I've found one exception: Red Barn near Arkona. Unlike most Ontario cherries, theirs are very dark red and almost black. The taste is not quite as amazing as the colour implies but it is good. The orchard is also a pleasant place to pick, because of the beautiful large trees which provide shade. Sturdy ladders are available, but not necessary, because many cherries can be picked from ground level. At least two other nearby farms also have good black sweet cherries.
I've never found especially good sour cherries in Ontario. They usually have very little taste other than sourness. So far, the best I've found are in the Arkona area. If you're there for picking sweet cherries, maybe also pick up some sour cherries, but don't expect too much. The cherries can be used to make a nice pie, and free pitting is available if you don't want to pit cherries yourself.
Some very good raspberries may be found in Ontario. They're available two time periods: early summer and late summer through early fall. However, not every place has raspberries during both periods. I've found good raspberries at Schoger Orchards and Awesome Berries & Gardens (where Northville Rd. ends at Townsend Line, near Arkona). The fall raspberries at Parks Blueberries were less tasty.
Note that raspberries are quite easy to grow yourself They're almost like a weed, spreading surprisingly fast via roots. Also, note that like with strawberries, very dark raspberries are overripe.
Blueberries may be the best fruit that Ontario has to offer. They cay be sweet and intensely tasty. Pick your own blueberries are available at Klassen Blueberries and Parks Blueberries.
I prefer Parks, because I've had a more consistently good experience with their blueberries. At Parks, you get a choice of up to four different varieties. I usually chose Bluecrop and I also like Reka.
At Klassen, there was never any choice in what variety to pick, and the blueberries were acidic and less tasty early in the season. However, later on I also found good blueberries at Klassen, and Klassen usually had a longer picking season.
Ontario is definitely capable of producing very good peaches. Unfortunately, such peaches are very rarely available. It seems like most farms pick unripe peaches and store them far too long. I've never seen pick your own peaches because peaches are too delicate. Considering all of this, it's probably better to buy peaches in a supermarket. If you want the best peaches, you need your own peach tree.
It seems that smell is a the best predictor for peach quality. Seek sweet peach smells and avoid acidic unripe smells or unpleasant subtle rot smells. In terms of colour, ignore the red, because even unripe peaches can be very red. Instead, check to see that the other parts are yellow or even yellow-orange and definitely not green.
Ontario can produce excellent apples. My favourite place for picking is Thiessen Orchards. They have plenty of varieties available in their large orchard. My favourites are Royal Gala and Honey Crisp. I used to like Golden Delicious, but apples from their current trees are less delicious than the ones I remember. In general, it seems that varieties which produce a smaller quantity produce more delicious apples. Note that while apple picking is easier and less time consuming because of the smaller size, that also means you save less money by picking your own.
Early apples are available starting around midsummer. They're usually sour, less sweet and with a less appealing texture than the familiar apples. However, around that time their freshness can make up for their inferiority.
Ontario grapes are often small, with tough skin and large seeds. This results in a lot of tough material, and relatively little of the desirable juicy flesh. Fortunately, it's possible to find seedless concord grapes which lack this problem. I highly recommend them, because they are very sweet and tasty. The taste contains some strong components which are not found in typical warm climate grapes in supermarkets, but I like those components.