Canadian Visiting US - question

My son is visiting a friend in the US and has been there since September 20 . He wants to stay his allowed 180 days but is wondering how long he has to come back to Canada before he's allowed back into the US again. He took a leave from his job which is coincidentally with the family company (it was just part-time temporary hours) and will have work if he decides to return. I can't seem to get a straight answer from anybody! Thank you!

Once he spends "a lot" of time in US, subsequent entries will be scrutinized.
There is no numerical limit on number of days one can be in US as a tourist in any year (either claendar of rolling period). the only restriction is that each entry is limited bt default to 183 days.

If he has insufficient proof of desire/need to return to canada, he will not be readmitted for any period.