The process is somewhat tedious, but not that difficult.
First stop
should be the Canada Customs Automated Import Reference System (AIRS), which allows you to enter the genus/species name to see the relevant regulations.
With the exception of Prunus and Pyrus, lots of fruiting trees and shrubs are admissible with only a phyto, which is provided by the originating nursery (there is almost always a charge for this).
Provided the plants don't require an additional import permit (again, discoverable via AIRS), you can get by with just the phyto.
At the border, it gets more confusing. You need to pull into the commercial vehicle holding area once through the border booth, and have to go to the office (where you'll wait with all the truckers), and fill out a form on the provided computer kiosks.
This involves a lot of information, including some specific codes and line items that can be intimidating the first time through.
The staff on hand will usually assist (somewhat) with this, but you have to have everything on the forms in order or they'll refuse to let you through.
You may or may not have an ag. inspector go through your load--if it's a lot of plants, expect to unload it all for them to have a look
Prunus is very difficult to import: you have to find a nursery willing to do the (to them) tedious and expensive treatments necessary to be admissible to Canada.
A few smaller nurseries in BC have been importing a lot of this stuff for a while, and pawpaws and certain fig varieties are available in B.C., sparing you the hassle.
Redhawk