I doubt of they would get bigger, but you might increase production. I always forage wild reds and blacks even though I grow about 20 domestic cultivars.They have a unique taste. I don't grow domestics anywhere near the wild ones, but brought in other wild berries to grow in my naturalized forest-edge garden. Thimbleberry, wine berry etc.

You would get bigger or longer or more canes, but not bigger berries. Many wild plants prefer poor soil conditions, so I wouldn't go overboard on fertilizer.

Thanks for the feedback. It seems there's little to be gained by cultivating wild berries.

I don't have the option of keeping domestics far away from these wild berries as they also grow on my adjacent neighbor's property.

"don't have the option of keeping domestics far away "

I would try anyway! Plants are fairly cheap.
At Indiana Berry they cost about $3.50 each. Oh you're in Canada. Nevermind!
My family still says the wild raspberry jam I made this year (I used a mixture of reds and blacks) was the best jam I ever made. So even though in the city I grow domestics, i still forage the wilds, blackberries too, but they are not as good. The wild raspberries taste nothing like domestics.The wild mulberries I forage are to die for too. Thye are my favorite. Not that good just eating, OK, but in jam or syrup, wow!