Hasan9999 said:
If your father's physical stay in Canada during last five years is less than 730 days, then he didn't maintain his residency obligation and lost his PR status.
No, he has not lost his PR status. The only way to lose PR status is to formally renounce it or have it formally revoked by CIC.
Mrs.Ahmad said:
By the time wo got citizenship aswell, but not my father, because he couldn't stay longer in Canada. Also his PR card got expired. Now he want to come to Canada but we dont know how and where to start his case?
He can fly to the US and enter Canada from a land border; this does not require a valid PR card. When he enters, he may or may not be reported by CBSA for breaching the RO.
If he is not reported, then he will be able to enter Canada, stay for 2 straight years until he once again complies with the RO and apply for a new PR card.
If he is reported, he can expect to have his PR status revoked, as he has no H&C reasons for staying outside of Canada. Once he loses PR status, he can be sponsored again. You haven't mentioned your mother; if they are still together and she is a Canadian citizen or PR, she can sponsor him. Otherwise, you would need to sponsor him, which will take many years.