Two types of Nav Canada charges - domestic and international.
For something small the domestic portion would probably be a quarterly charge; they are for anything up to 3MT and there are two bands. IIRC C$30 or C$60 ish.
The international charge is in two parts; enroute and comms.....it's the same charge for any size aircraft and around C$160 total.
Don't forget the Denmark and Iceland charges (collected by the CAA) which are £19.68 per leg that involves Denmark (Greenland) or Iceland.
Check your ferry contract to see if you, or the company, are liable. A reputable ferry company takes care of this and has an ICAO callsign/flight number so that customers are not bothered with this stuff
Nav Canada and the CAA will take a credit card by fax to pay for these bills - so at least you don't pay wire charges.