This would only be of note if you plan to retire in your original country of origin, in your case France.
There is an agreement between France and several countries including Canada. Once you will retire, if you have worked 10 years in Canada and 30 years in France, then you will get 3/4 of your money from the French Pension plan, and 1/4 from the Canadian one.
This agreement works whether you are French or Canadian.
But, that said you can put a lot of money into TFSAs and RRSPs.
I came to the same conclusion unfortunately. Would gladly pay to contribute to CPP on the assumption that I'll (probably) be retiring back home. Unsure how it is in France, but in Canada (for now), I believe future CPP payouts are based on contributions made today (i.e. supposedly we are paying our future retired selves). This is unlike the US social system where current payouts are based on contributions made with today's generation of workers.
>>But, that said you can put a lot of money into TFSAs and RRSPs.
I'm not an accountant or a lawyer, but my understanding is that unless you have contribution room left for your TFSA or RRSP prior to your departure from Canada, there's little point to contribute since the "contributions" will not be recognized as such and hence the tax "benefits" in both cases will also go unrecognized. I think the only exception is for Canadian income (e.g. rental property).
Transferring funds into Canadian TFSA/RRSP accounts may be possible, but the CRA will eventually ask for a reckoning unless your friends are willing to roll the dice. Based on personal experience, penalties and interest per year add up quickly.
I think you're conflating the basis for calculating the payouts you will receive, and the sources of payouts. I. e. most government pension schemes are use today's payments for today's pensioners, but will still give you a higher pension if you paid more/longer into the system.