follow the instructions in the letter
I do not know the answer - the problem
might be if the instructions are not specific to Brazil, they may only say "If you require a visa to enter Canada do [details]; If you do not require a visa, [different details.]"
And Brazil at least is a special case - visas waived/ETA possible for citizens that meet a few criteria but all others must get visa.
Worse, the govt "do I need a visa" tool does not give the choice for purpose of visit of 'land as an immigrant.'
So it is not clear to me (unless the passport request letter has more details).
My suggestion would be to check/confirm with the visa application centre under the 'submit passport and other documents.' And hope one can get a straight answer or confirmation. (If the visa office responds to emails, another option)
Failing getting a clear answer, I'd submit the passport
as if a new visa will be needed - and then the visa office in the embassy will either insert a visa or return with confirmation that the ETA is sufficient. (Certainly the visa office itself will know what is required)
Good luck.