WealthSimple is still functioning fine here in Canada. They're probably just overloading their servers.

can't even access my vanguard account. Hearing reports from friends/family across the board that they can't access their financial accounts. Fidelity, Schwab, more.

I maintain accounts on Robinhood, TD, and Interactive Brokers.

Typically, Robinhood is always down at market open (even on low volume days).

On high volume days, IB has been down several times.

However, the thinkorswim platform on TD is great and I've yet to encounter downtime.

Interactive Brokers seem cheap and have APIs and apps for everything.