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If I am not wrong when your friend landed as PR in Canada he was having Valid H1B visa, DID CANADA IMMIGRATION ASK HIM about this? NO , they are not intresred in other Visa stamps on ypou passport.
If his H1b is expiring in Oct 1, he should file immidiatly for the Extension and it will take 60-90 days to recieve his H1B approval from service centre.IF he extends H1B he will have NO problem from Canada immigration.He should ONLY be concerned, how to maintain his Canada PR(IF he/she wishes) as he will be working in US and will be out of Canada for more than 183days and may loose his PR according to present law .