As a Canadian in a happy relationship with an American, we quickly realised the difference that you've pointed out. We also realised that I had a tinge of the stereotypical Canadian "sooorry" sound, so we ran with it. If it's a situation where one of us intends to express remorse for a situation occurring, we slightly intonate towards the "o" sound, and for situations where we're accepting blame, we edge towards the American "sarry" (again, over emphasized to get the point across). It's subtle, but it's worked well for us.