Canadian here.
I'm unsure of the Canadian tax treatment of 401ks, although I suspect
existing balances will be treated similar to a Canadian retirement account, as I know the tax treaty between US/Canada has some recognition of each country's retirement arrangements.
If you become a Canadian resident or citizen and have earned income in Canada, you will generate room in the Canadian equivalent of 401ks: the RRSP. RRSPs are simpler than American 401ks and you can open one independently without any involvement from your employer. The RRSP is recognized by the USA for tax purposes. Dividends I earn from US ETFs, for example, are not subject to US withholding tax in my RRSP.
I found a brief article on this here:
https://business.financialpost.com/personal-finance/retirement/rrsp/why-the-rrsp-is-the-best-retirement-plan-out-there-for-the-dual-citizen-living-in-canadaYou will also be able to use the Canadian TFSA. TFSA contributions are made with post-tax money, but the growth and withdrawals are tax-free. However, TFSAs are apparently not recognized by the USA under the current tax treaty, so if you retain your US citizenship then it's not worthwhile.
There is, as far as I know, no equivalent to HSAs in Canada. I don't know why you would need one if you have Canadian health care.