No experience with bikes on BC ferries - but a lot in the Maritimes, on a variety of bikes.
On rivers, the ferries usually run flat & smooth and there is no need to worry about tie-downs. Make sure to leave the bike in gear so it does not roll of the sidestand.
I prefer sidestand to centerstand, because the 3-points - stand and wheels - provide wider (more stable) base in all directions than the centerstand.
On crossings that get waves (like St. Lawrence River in QC), I use a ratchet strap to lock the sidestand to the rim of front wheel. That way, I assure that the bike does not pitch abruptly and roll off. Also, occasionally, I have locked the brake: a velcro strap tightly wound around front brake lever. Great parking brake.
If you are planning on a really wavy crossing (like going to Victoria, for example), be prepared to tie down your bike. Usually, the crew will instruct you to do so. I carry my own straps for that purpose - I either tie the bike down with them or at least use them to extend the provided straps or ropes: these tend to be grimy and soaked with oil. I also carry disposable gloves (yes, I know it is feeble, so?) - that way I do not have to ride the rest of the day with hands and gloves reeking of diesel.
Rarely, on some ferries, the crew will insist on pulling a strap across the seat. I usually try to discourage that, as it stresses the stand - and does not help anyway, since the bike settles on shocks.
Also, as mwnahas
posted: make sure no helpful crew member ties down your handlebars!
Here is an example for turbulent crossings: 2 straps up front, one from the rear wheel, on a ferry to Goose Bay, Labrador.
In picture above, the front straps are attached to the crash bar - not really applicable to the LT. For the Light Truck, it's best to go to the front fork brace, as demonstrated on this Newfoundland ferry crossing. You can see the strap pulling the rear wheel.
Notice how I extended the crew's straps with mine.
But, as I wrote, if you are only going to use river ferries, there should be no issue (though the brake lock won't hurt). Just park the damn thing.
Look at what the other riders do and follow their example.