There will always be some abuse of services. It just turns out to be negligible most of the time. The benefits will far outweigh the losses. Also - people shop for services all the time. If they want to move to a province that has better benefits, that would be normal and smart. If the program ends up being mostly federal, this won’t be as much of an issue as things will be more standardized, though.
I don’t think Twitter and Reddit are going to die quickly. They have user bases that they can monetize and bots to flood content. They were shitty enough that enough of left and gave a nice boost to federated platforms. That boost will grow every time those legacy platforms alienate their users by treating them badly. Like windows and Linux.