There are no rules against it, but it may bring questions as to your physical presence claimed, especially if you applied with little extra days from minimum, or if you already spent extended amounts of time out of Canada in the 5-year period etc.
Obviously, there is also the cost to consider (seems you are aware of that), given you have to fly last minute to Canada for test/interview and then oath OR fingerprints even (depends on where you are, sometimes that can be done abroad).
You might also want to consider where your physical mail is going in Canada, as they might send notifications through mail rather than email, and if yours is not being checked regularly you might miss important communication.