It's too early for apples. My local Loblaw-group-of-companies grocery store just a few weeks ago finished selling Ontario bagged Macintosh apples... from last year's crop (apples keep for a long time if stored properly). Now it's a matter of waiting for this year's crop this fall. Apples are more likely to come from Brampton than from Niagara fruit country anyway.
The same store is now carrying Niagara peaches, plums, and cucumbers (and more, I'm sure). The season for Niagara strawberries and cherries has already passed, so it's back to California for those items. They just got some local corn, but it's still too early and doesn't compare in quality to the US stuff.
The selling of local produce hasn't gone away, but people's expectation to walk in to a store 52 weeks a year and see the same products has distorted perceptions. Previous generations would have known the 3 or 4 weeks of the year when they could get strawberries or cherries or whatever, and frozen or preserved a supply for the rest of the year. These days consumers have no concept of "seasonal produce".
From what I understand, the biggest problem is the Ontario suppliers simply cannot reliabily supply the volume of product that major retailers demand. Loblaw National Grocers could order (I'm guessing here) tens of millions of pounds of blueberries over the course of a year from an American supplier who has thousands and thousands of acres of farms throughout the US and can supply year-round. Or they could get it from an Ontario supplier for a few weeks out of the year, who is counting on weather to determine when the product will be ready or if it well ever be ready at all and still have to deal with that American supplier for the other 46 or so weeks of the year.