Hi Kym ~
Paris CDG is fine for trains to St. Jean PdP. There are a couple of trains that connect directly from the airport to Bayonne, and from there you transfer to the St Jean train. You have additional options if you go into Paris for your connection.
I'm in the Western U.S., which I assume has similar connection issues as your location in Western Canada and I've used Paris, London, and Madrid as my main Europe hubs. They each have advantages/disadvantages. My priorities have generally been a) fewest connections and b) cheapest price. Here's how they stack up:
London Heathrow -- easy non-stops from Seattle and many places, and London works ok to access St. Jean (via Biarritz) and ok for the return from Santiago (with direct flights in season). The disadvantage is that international flights use Heathrow, but the other flights use Stansted airport or Gatwick, both of which mean a cross-town ground connection which adds time and sometimes an overnight.
Paris CDG -- easy non-stops from Seattle and many places, too, with either trains to Bayonne or flights to Biarritz for a fairly quick ground connection to Bayonne's train station. Getting back from Santiago is a little more complicated -- by train it means several transfers, and by plane it means a transfer either at Madrid or Barcelona since there are no direct Santiago to Paris flights.
Madrid -- no non-stops available from Seattle, so generally a transfer at JFK or Chicago, etc. From Madrid to St. Jean means a train to Pamplona (flights are available but costly) and then a van to St. Jean (which is not bad at all). From Santiago to Madrid is quite simple via train, bus or air with multiple direct options.
In general, for people off the Continent there's no simple incoming plane itinerary for St. Jean, while the outgoing itinerary is easiest (in my opinion) via Madrid.
Hope some of this helps. Buen camino!