RRSP — the one the treaty covers
Article XVIII(7) of the 1980 convention provides for an election to defer US tax on income accruing inside the plan, and Rev. Proc. 2014-55 made that deferral automatic for eligible individuals — which is why Form 8891 is no longer filed.
Deferral is not exemption. The account is still reported on the FBAR and, above the thresholds, on Form 8938, and distributions are taxable when they come out.