Got an Ontario watermelon this year. It was cheap and perfect. The other 2-3 were from Florida I think, and pretty much rotten when I cut them open

Yes, but they will be on the shelves late(r) it seems (Maybe different for eastern provinces?). In BC I only saw them late August/early Sept this year I think and since it's end of the season for other suppliers, no good deals.
Mexico is usually already June if not earlier, even some deals to be had, usually found them to be easier to spot a good one and on average were better than US ones so I've been avoiding US even before turd2.

Edit: FWIW I mostly either see Mexican or some other foreign workers on farms, so I have my doubts they are treated particularly well. Ive seen some of the accommodations they have on farms (like those portable container size boxes at constructions, foremen? use as offices), they usually go to shop in groups, so I guess not much freedom or high enough pay to do what they want. I therefore don't feel super inclined to buy only "Canadian" in that department. Meanwhile there are plenty of mansions being built up at various farms around lower mainland...

We often get watermelons from Ontario in Quebec, sold at grocery stores. Bought one 2 weeks ago, the whole thing for 2.99. The only hassle was carrying it over 2 km in my backpack.

I've recently saw grown in Canada sold at Costco here.

Yes, but who knows if they are distributed to your particular grocery store.

It really depends where you are. I found them at a local farm market. Unfortunately only got out there once. I have see some from Mexico but only at certain times a year.

Thought about pickles earlier... you can only get pickles from the USA or India. INDIA. Do they even eat dill garlic pickles out there? Why are they preparing them? Why cant Canada make their own effing pickles?!