Why do you think this is not already the case? Just curious, because it seems like many people in my birth province of Alberta aren't aware that we already have these pipelines, and think that people here in Ontario and in Quebec are burning Saudi oil.
Line 9 runs practically right behind my house, and since it was reversed some years ago it feeds facilities in Ontario (and Quebec) with Alberta oil. Line 5 runs under the great lakes, all the way from western Canada to refineries in Sarnia (and is currently under threat from Mich. governor, but that's a separate topic)
90ish percent of Ontario's oil consumption is domestic oil depending on time of year and so on. The remainder is mostly from the US. Small % from middle east.
Oil from Alberta makes it all the way to refineries near Montreal. Last I looked 70% of Quebec's oil is domestic origin.
Politicians in Alberta have become masters of ignoring this key fact in their rabble rousing.
Could capacity be increased? Maybe. Is it strictly necessary? I don't know. Should we be reducing consumption anyways? Yes.
See map here, on Enbridge's website, zoom in to Ontario:
https://www.enbridge.com/reports/2021-liquids-pipelines-cust...
Now, the Atlantic provinces, that's another story. But a much smaller market.