Having checked prices many times over most of the different companies and comparison sites it's not always cheaper (never in my findings, apart from the one time Total Rewards had those great deals which disappeared rapidly) booking with a US site. Both British Airways and Virgin Atlantic have car hire only and prices are excellent, includes all taxes and fees and insurance. The enhanced insurance may only be necessary if you haven't got travel insurance. Anyone outside the US can book and I'm pretty sure that includes Canadians. Obviously check before booking just in case things. Hotels can also be cheaper so always worth checking.