That's why I'm personally shorting GBPCAD instead - it's not in strange territory, but has around 800-1000 pips to go before it gets to last year's support level. It's inching down slowly - because GBPUSD is creeping back towards the 2.01 resistance level, offsetting the USDCAD freefall - but IMHO more reliably. When USDCAD starts recovering, it will be time for GBPUSD to start climbing down again (I think Blair's resignation, with it the change of Chancellors and political uncertainty in general will more than offset the small difference (.25%) in interest rates. The market didn't even notice the last British rate hike on May 10 - the same day Blair announced his resignation date.
In the meantime I've taken a timeout from GBPCAD and put my chips on another big USDJPY unwind. I shorted at 121.94, predict 117 in a few weeks.
May long USDCAD in July sometime, if (as I think) Canadian economic data weaken because of the strong loonie and as our biggest customer heads into recession. It will be a lousy summer for the Canadian tourist industry, that's for sure (high gas prices on top of everything). Probably not great for resources or manufacturing, either. So for me, it's time, not price, that's the main factor. Wait till the fundamentals are right and a decent uptrend is established.