Read through the reciprocal agreement that @Dana posted. There’s been a lot of misinformation about this, but it’s spelled out pretty clearly.
Canadian horses showing in USEF shows do not need to be microchipped until December 2025. If you want to get it done to be safe, or to get it out of the way, then go for it.
You do need a USEF number and you need to complete Safe Sport. Give yourself time, it takes longer than going through the EC stuff.
If any Canadian athlete/owner plans to compete their horse in the US at USEF competitions and WILL NOT be collecting points/awards with USEF – you can log onto the USEF website ( https://www.usef.org/ ), create an account (if you previously do not have one) and obtain a Competing Membership for $0. You MUST select the option of competing using the EC/USEF Reciprocal Agreement – you will need to provide the renewed Equestrian Canada Sport Licence #.
My advice is to have the reciprocal agreement printed or saved to your phone just in case. However, lots of Canadians show at WEC Ohio so the office is pretty familiar with this stuff.