Go in the summer time...like July.
Thanks for all the replies, they were really helpful!
I've lived in BC for most of my life, with some time spent living in California and Japan. I can definitely say that living in those two places were far better for fruit. Where I'm living right now, the snow covers the ground for 6 months of the year, and the most available fruit are apples and pears. Now, I'm a bit jaded, because i don't particularly like apples and pears and it's difficult to eat enough of them. Bananas, dates, oranges, mangoes, etc, do not grow here. Sometimes you can get them cheap. I only buy organic, so things are rarely cheap... mangoes cost like $2 per mango in the winter. Bananas cost me approximately $35 a box from a eco-ravaging company like chiquita (organic though), and $45 a box fair trade organic. I can get a 5kg box of medjool dates for about 80 dollars.
I'm coming at this subject from a local and environmental view, because I'm an organic farmer. Can you get tropical fruit in Canada? Of course you can, it's a 1st world country, you can get rocks from the moon in Canada if you desperately wanted. It may cost you, it may not, really depends on where you are. Personally, I'd rather be on a tropical beach somewhere, sipping on a locally made pina-colada and ravaging my liver than eating 3000 cals of apples and pears.
Summer is pretty great though, I will admit that. Blackberries, strawberries, raspberries and blueberries... Peaches, nectarines and plums - especially where I live, right next door to the Okanagan, the fruit-basket of BC. Hiking and outdoor sports are great in the summer, and the waterscapes are breathtaking in their own wild way, so that combined with the increased availability of fruit would definitely make it the only worthwhile time to visit unless you have family or friends here.
You can probably tell I really want to get out of here :P But summer is coming... oh, please, gods, let summer come...
It really depends on where you go. If you are looking for great quality and variety then only come to Winnipeg during the summer months :P