カナダの企業にフルタイムで雇用されていれば、海外在住でもPRは失効しません。
http://www.cic.gc.ca/english/information/applications/guides/5529ETOC.asp
B. Employment outside Canada
Acceptable employment
Each day that you are working outside Canada is considered a day for which you satisfy the residency obligation provided that your employment meets the following criteria. You are an employee of, or under contract to, a Canadian business or the public service of Canada or of a province, and are assigned on a full-time basis to:
a position outside Canada;
an affiliated enterprise outside Canada; or
a client of the Canadian business or the public service outside Canada.
Canadian business
For the purposes of this application, a Canadian business is defined as:
a corporation that is incorporated under the laws of Canada or of a province and that has an ongoing operation in Canada; or
an enterprise that has an ongoing operation in Canada and is capable of generating revenue and is carried out in anticipation of profit, and in which a majority of voting or ownership interests is held by Canadian citizens, permanent residents, or Canadian businesses as defined above; or
an organization or enterprise created by the laws of Canada or a province.
Evidence of acceptable employment
You must provide supporting documents indicating that your employment outside of Canada meets the requirements of the residency obligation. Refer to the Document Checklist (IMM 5627) (PDF, 121 KB) for a list of supporting documents.
ここからは裏技(独り言)です。
実行する場合は自己責任で。
会社(法人)を持っている知り合いのに頼み込んで、
その会社に勤めていることにして、給与を定期的に銀行口座へ振込みしてもらう。
振り込んでもらった分はなんらかの形でその人へ返す前提で話をしておく。
Taxリターンも、毎年カナダ側できちんと行っておく。
PRカード更新のときは数ヶ月ほどカナダに戻り、必要書類を提出。
これで日本に長期滞在していてもPRカードが更新できるかと思います。
あくまでも自己責任で。