A new startup ISP won't be peering, they'll be paying an incumbent provider for at least transit if not full access services (e.g. "dedicated internet access," basically commercial ISP service under contract terms that allow diverse uses including internet services). The term "backbone" is pretty useful here as the number of providers in North America with real global connectivity is fairly small; most ISPs with under thousands of customers are themselves customers of Centurylink/Lumen or Verizon, both of which have been steadily acquiring their competition in core internet connectivity (Level3 for example).
You don't need to buy DIA from an incumbent. You can get L1 / L2 circuits from various carriers back to data centres where you can buy transit and peer with other ISPs using BGP. L1 wavelength circuits did not suffer from the outage Rogers had yesterday, but the downside of wavelengths is that they require physical intervention to recover from failures.
For exchanges, Ontario has the Torix exchange in Toronto for peering, and there's QIX in Montreal. Ottawa has Ottix, but it does not have many peers. There are others out west (as I'm in Ontario and don't pay attention to them as much).
Torix has most of the peers you need for a majority of an ISP's traffic.
Most consumer traffic is going to be to CDNs (Limelight, Akamai, Cloudflare), AWS, Apple, Google/Youtube, Microsoft, Netflix and the like if you're not big enough to have a private interconnect to them. It turns out the big internet companies like IX's too and don't want backbone providers being gatekeeper.
