The procedure is fairly straight forward: Go into any flight school and they can compare your hours to the TC CPL matrix. They'll identify what you need and put a plan in place for you to achieve your goals. You can also do this yourself by googling "Transport Canada CPL requirements" and do the legwork yourself, which might save you a buck or two.
With only 900 hours you are ineligible to hold a Canadian ATPL. You're at least 600 hours short on total time, not to mention what you're short on for PIC, X-Country, Night, etc. Therefore, worry about your CPL conversion first and then worry about your ATPL exams. There is no such thing as a "frozen ATPL" here in Canada, so doing the swat and writing the "A's" now really does not help you unless you're hoping to go back onto a transport category aircraft - but again, focus on one thing at a time.
As for the type rating. There are only a handful of companies that operate those in Canada and the majority of companies here don't really care if you've got a type rating, as you've got to go through initial training to get the PPC anyways (which is not the same as the type rating). It might come off as harsh, but really all you're doing is saying "look how cool I am with 900 hours and a 757 type rating." That doesn't go over very well here, as it comes off as being a "tall poppy." You're probably not, but that's why we say "perception is reality."
Now, the 757 does show that you've got some heavy jet experience, but most Canadian airlines would look at that to say you've got some two-crew experience rather than heavy jet time. It just doesn't count the same here as it does across the pond...at least, for now.
Oral exams. Not really. They'll throw a couple questions at the beginning of any ride, be it type or basic IR questions, but it is a component of the ride rather than a separate exam that must be passed prior to the ride. You'll find your initial IR will have the most questions, decreasing in number but increasing in intensity as you go through your career. For example, you're unlikely to be asked what the difference between RNAV 1 and RNAV 2 is during your initial, but you might be asked during a recurrent with an airline - and be expected to expand on any operational considerations.
I hope some of this helped, and best of luck!