To use a heat pump up there, I would first have to say that the house needs to be well insulated and well sealed.
I would not use them on some drafty shack.
I am going to buck the trend here but first I am going to explain why.
I did a fair bit of ground source in NW Ontario, and the winter design temperatures were a lot colder than Vancouver. I sized this equipment for 70 to 80% of the heat load and for cooling they were easily 50 to 100% oversized.
Never experienced a summer humidity problem, because the latent load was not there in the ambient air.
The cooling season was not that long and the summer dewpoints were not overly high. Vancouver has a lot milder winter, but the humidity in the summer does not look much worse than NW Ontario. It looks like 61F is a worst case dewpoint there in Vancouver.
I would look at the heat output of the units when the outside temp was at about freezing, and size the unit to heat the house at that temperature. Make sure the heat strips can handle the whole heating load when it drops down to your design temp which has to be in say the high teens.
Probably half the heat strips in auxiliary would supplement the heat pump and keep the place heated during design days, and the second bank could be used in emergency should the compressor fail.
I did the ground source with duct heaters, never did the air source with the strips. Sometimes the Geo jobs were two hours out of town and when you got a call at 2AM for no heat, it was nice to tell them to put it on emergency and they were warm until you were there the next day to see what was wrong.
Air Source heat pumps were not viable in NW ontario, but should do pretty good where you are.
The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.
Thanks for the input guys, especially Carnak, the systems I am currently designing are ground source heatpumps. I will size it to the requirements for heating unless it makes my cooling grossly oversized. Cooling in our area amounts to a couple of weeks a year. For the most part our temps don't drop below freezing during the day. In our area we size to 7 degrees farenheit but most years we never see that cold. average winter temps are well above freezing for weeks at a time. I will add heat strips and stage them so that only on the coldest days should they ever come on full.