Hi,
I'm no expert but my thoughts are-
If I was going to be driving on roads rough enough to warrant a suspension lift, I would worry about mounting a bike rack to the door of my van. All the weight of the bikes will be on the sheet metal, and four bikes weigh a fair bit, especially since the outside ones will be exerting a bit of leverage on the frame of the rack.
I have a Maxxraxx bike rack- it bolts to a towbar flange, which makes it pretty secure and also means the towball is free for a trailer (boats!).
You might even consider putting a rack on top of a trailer and towing them. That would be very expensive to set up, though, unless you already have one!
Maxxraxx: http://www.maxxraxx.co.uk
I dare say they would ship to Canada, if they or an equivalent is not available locally.
Have a look at the website to understand their selling points. Even if you don't want one of these it may help you to cIarify what you do want!
They have a couple of handy features that are hard to find: you can fit extra brackets to other cars, to make it easy to swap the rack over and, of course, you can still use the hitch!
Cheers,
W.