Welcome to the forum!
Lots of ways to do it. You need to pick a euro gateway city. From Toronto, you have a few choices, London, Paris, Madrid are all popular. I like Paris, but see what prices look like elsewhere on the days you are going.
From Paris, you have two choices. Catch a connecting flight to Biarritz (BIQ) either from CDG, or take a RER train or the shuttle bus to Orly - the other Paris airport. There are more flights to BIQ out of Orly than CDG. From BIQ, you can take a city bus (1/2 hour) to Bayonne and pick up the SJPP train, or you can book Express Bourricot that operates a shared ride service to SJPP. The train is cheaper of course, but the shared ride is the easiest.
Alternatively, (and my favorite) catch a train from Paris to Bayonne, connecting to SJPP. I recommend a few days stay over in Paris if your budget can handle it, its a city not to be missed if you've never been there. AFter a day or two visiting Notre Dame and the other sights, catch a TGV train from Montparnasse station to SJPP via Bayonne. Cheap and fast. If a stayover doesn't fit the schedule or the budget, you can catch a train to SJPP directly from CDG, but its a LONG travel day. Best place to figure out the SNCF (French) train system and buy train tickets in Canada is trainline.eu.
Buen Camino!