A quick google search shows mixed results, some people being able to use 401k for POF.
Per IRCC:
"
Funds must be readily available to you. For example, you can't use equity on real property as proof of settlement funds.
The funds must be available both when you apply and when (if) we issue you a permanent resident visa. You must prove to an immigration officer that you can legally access them to use to settle here when you arrive.
"
It seems to depend on the officer's interpretation of readily available, and if they consider 401k balances to fall under that category.
You'll definitely need the funds liquid when you move (if approved) anyway.
I see two options:
1) Submit your 401k balance when applying, if they have concerns they'll reach out to you, at that point you can liquidate the amount needed and reply to IRCC's concern.
2) Liquidate the amount needed now and apply, you pay taxes & penalty but you get peace of mind throughout the process.
