Wealthsimple is only licensed to open Canadian accounts for residents of Canada. If you become a non-resident of Canada for tax purposes, you'll need to withdraw or transfer out your GRSP funds – even if you are still employed by the same company.
Note: This is a limitation of Wealthsimple rather than an investment regulation, so you can hold your Canadian accounts at another institution that supports them.
Withdraw option: Cash out the assets in your GRSP and take the money with you. Keep in mind that you will permanently lose that contribution room and withdrawals or transfers as a non-resident of Canada may be subject to a Canadian non-resident withholding tax of 25%. Depending on your new country of residence, this rate may be lower depending on the tax rules of the new country. It’s important to look into the implications of timing, foreign tax credits and more to make sure you can avoid being taxed twice (i.e. once by Canada and then again in your new residence).
In the US, for example, there is no way to directly transfer an RRSP into an IRA (individual retirement account) such as a 401(k) and maintain the tax-deferred status. You would have to withdraw the funds from your RRSP and pay applicable taxes, then make a separate contribution to an IRA in the US. When it comes time to retire, you will have to pay taxes to withdraw those funds as income, which means you’re paying taxes on that money a second time.
You can get help through this withdrawing funds from Invest help article.