If you leave no assets behind, there isn't much they can do against you personally. They might harass or try to intimidate family members or close associates to persuade you to return or settle your debt, but that's usually just smoke and mirrors. Not sure if I've CRA do that, but have seen it from a few others.
Any assets you do leave behind can be seized up to the value of the tax debt (plus fines and interest).
The CRA can in some circumstances do a third-party assessment and declare another person liable for your tax debt.
If your tax non-payment turns into something more serious (money laundering, fraud), then Canada's options increase and you could for example face extradition.
So it depends on your circumstances.
US famously refuses to renew passports for citizens with significant tax debts. Canada often mirrors what US does, but it hasn't done copied that particular policy yet, AFAIK.