Yes, as long as the 7-Eleven phone is unlocked. So far, users have indicated that all phones but the 2610 are unlocked, although there was even a report of a 2610 that was indeed unlocked...
PC phones don't have SIM cards, so there's no way of transferring that plan to a Rogers phone.
Luckily, 7-Eleven runs on the Rogers network, so you should be able to swap a 7-Eleven SIM card to a Rogers phone. (Otherwise, you would need to unlock the Rogers phone.)
As for Petro Canada, it runs on the Rogers network as well, from what I know. But perhaps someone else can confirm that fact.
11:57 pm
We have a Nokia 1600 from rogers PAYG which my teenage son has lost the charger to. If I was to use the $100 phone deal and pick up a second 1600 (for my other son), could I get 2 - $50 vouchers and then change the original 1600 over to 7-11? I don't really understand the process here. The one I buy will be on the 7-11 system so do I phone them to switch the other over and hopefully keep the same phone # for it? This would be great as my second son could use a phone nad we need the charger too, a win all round I'd say.