I don't think the Canadian Govt rate is available to US Govt (I've tried booking govt rate in other countries via phone before, but was told US ID does not apply...Still, you may get lucky and they may not ask for ID at all (I seldom get asked to show it, anyway)..I'd say book two rooms, one at the lowest avail rate (just in case), and one at the Can Govt rate, but play dumb if they reject your US ID at check-in...good luck!