The two main charter wreck dives in Nanaimo, the HMSC Saskatchewan and Cape Breton are both at around 100 feet depth. It can be cold and the vis low and possibly currents. This would be slightly different to the lakes that you certified in with some slight simlarities. There are other really cool shore dives in Nanaimo also, but depending on what you want to do, you will find yourself below 60 feet quickly.
I would recommend getting in some practice and the AOW course while in the calgary area. During your AOW, I would say that Night, Nav, Deep, Drysuit and Search and Recovery are among the better ones, unless you can do wreck, then replace S&R with wreck. This will give you experience with the things you will need to be comfortable on the sort of dives found in the Nanaimo area, including some exposure to depth and narcosis, plenty of practice with navigation skills, getting comfortable around wrecksl experience with lights and lower visibilities and most importantly, warm and dry in a drysuit. Depending on the charter boat, they may or may not have a heated cabin on the boat, and being on a open boat after a dive in a wetsuit is not only crazy, its an easy way to get hypothermic, especially in the Pacific Northwest.
When you get there, make sure you take some serious time and figure out your buoyancy in saltwater, as it is quite different compared to fresh. I would recommend trying to get some shore diving in before you hit a charter boat so that you can get in some saltwater practice before you drop off the boat see the wrecks, it will make you that much more confident in the water making the expensive charter dives that much better. There is a nice site for this called Madrona point, gorgeous shore dive with easy entry so you can get in and out to adjust your weight.
Anyway, that's my two bits.