Well, it's a good point. The country shouldn't be relying on only two big companies for its infrastructure. This honestly should serve as a wakeup call.
It's a bit more complex than that.
rogers et al provide the retail infrastructure i.e access that gets sold to the customer whether a home or a busienss but there are also providers involved who deal at the wholesale level i.e to the ISPs and provide the really big "pipes" that shifts the data around.
At the retail end, competition in that it can help (in theory) keep prices down but it can't help in situations like this. There is no easy way for customers simply to change providers and advancements in internet technology have made it this way.
For home users, Dialup was easier, get another provider, net account and change the number you dial but that technology is pretty much dead, DSL was could be done by needed some-one to go the exchange and re-patch the DSLAM but with cable and fibre? forget it.
Businesses are more complex because can also be dealing with DNS and IP address issues for e-mail, remote access etc.
If my understanding is correct, the problem was that traffic couldn't be routed in and out of the rogers network. so if you were a customer with Interact who used Bell but your debit machine provider was with Rogers you couldn't connect to complete the transaction. If you were lucky and both ends where with rogers then things might still work (for example my local Freshco could use debit if you were with TD Bank).
In this situation all the ISPs in the world wouldn't have made any difference because there's no way for either end to quicky and easily shift.
And when there's an outage that means the rest of the world doesn't know about about your networks (or autonomous systems as they're known in BGP) having multiple providers for your really big pipes doesn't help.
Network engineering isn't my background (more small level system administration) so I can't really think of a solution but know the answer isn't easy and I don't think the requirement from the feds for the ISPs to work together is will be worth a pitcher of camel spit because of the complexities involved.