Seems like you CAN use other oils without any warranty issues. Page 38 of the Service Manual says “Use BRP XP-S 5W 40 synthetic oil (P/N 293 600 039) or an equivalent motorcycle oil meeting the requirements for API service SL, SJ, SH, or SG classification.”
Seems pretty clear to me
Amsoil, Royal Purple, Castrol, Mobile 1, etc. are all "legal" but keep good records