Hi chtucker,
From your question, I'll assume that you are using the US S-57 charts in your TZT. Both Navionics and C-Map are provide good coverage for the area you are interested in. Frankly, Navionics or Jeppesen have essentially the same information and are presented very similarly on TZT plotters.
MapMedia, the company that actually produces the charts for TZT, formats Navionics and Jeppesen data into a proprietary format used by Furuno, MaxSea and Nobeltec. What this means for you is that S-57, Navionics and C-Map charts essentially look the same on the TZT plotters.
The most cost effective solution for nautical charts for your cruising area would be MM3-VNA-025, combined with the NOAA S-57 charts. Keep in mind, though, that you will have to switch between S-57 and Jeppesen in the Chart Management Menu upon leaving US into Canadian waters and visa versa.
The Jeppesen chart are, MM3-VNA-035, provides coverage for Alaska, western Canada, the west coast of The United States and the west coast of Mexico.
Finally, as you stated, the Navionics based charts would entail purchasing three chart reasons just for Canada.
Please forgive the rather long winded explanation; however, the subject is a bit complicated.