Actually, it has nothing to do with UA vs AC. The agent was probably right that this is way over MPM; but you should explore if a published routing exists which would make this possible (you will probably need to lose PVG, though). I guess you would need to lose SEA, as well, as likely the published routing will be through LAX or something.

Regarding the MPM - it's MPM+5%, and you can SORT OF calculate using gcmap, it's mostly accurate.

So my suggestion - first, figure out the valid published routings on MEL-YYZ.