Most of it will probably be subject to tax.
You can shelter a portion in a LIRA using a formula based on age and the annual benefit. At age 53, it is 10*benefit. If there is RRSP room, then you can fill that up, but the rest gets taxed, and most of it will be taxed at the highest marginal rate.
If half of it is taxable, then over $500k will be lost to taxes in Ontario. 30% will be withheld up front, the rest will have to be paid later - Dec 15 if he already has installment requirements, or following April 30.
Usually you cannot take a commuted value withdrawal if you qualify to collect a pension, but the rules depend on the individual pension plan and provincial, or federal, regulations. Depends on which jurisdictions' rules govern the plan.
If he has 30 years in, I'm guessing he's in his mid-to-late 50s. Probably best to take the pension. Just take a good survivor benefit option.
(Says the guy who took a somewhat smaller commuted value payout at 53. But then I didn't qualify for an unreduced pension for 7 more years.)
Al