A couple of suggestions. First, make an appointment with RBC and feel the situation out with them. If your debt to income ratios will work, they are probably your best bet. In a "feeling it out" scenario and "asking for advice", you will probably be able to get them to do a soft inquiry on your bureau, which will not affect your score, and they should be able to work with you from there.
Otherwise, you will need to deal with a mortgage broker. Getting a score approaching 650 will make it considerably easier for them to get you a prime loan, but call some and ask them. With a mortgage broker, you will need to run your own Transunion and Equifax scores and bureaus and take them in with you. They should be able to feel out your contacts and give you a rough idea whether they can help you or not.
A quick fix for your credit score... if you're carrying a balance of more than 30% on your card, pay it off first. Paying off your card will boost your score in 30 days.
Unfortunately the US credit crunch is hurting the ability of marginal people in Canada to get credit as well, so it will likely be more difficult for you than it was for me.