You were saying maybe we never had PR or citizenship and came over on a working visa, how long would we have been able to stay in Canada then on a working visa.
I don't know how it was back then but they have just recently set some new rules that limit work permits being extended for more time than a maximum of 4 years. Before that, you could have extended indefinitely as long as the employer had always been able to prove that they found no Canadian for the job.
I think it is likely that they were PR's. Start by using the link I gave to have them look for your citizenship records. If they don't find any, then you are not a citizen.
If you were not a citizen and want to find out if you were a PR, you will need to find if you had an Immigrant Visa and Record of Landing (IMM 1000)/Confirmation of Permanent Residence (IMM 5292), see
http://www.cic.gc.ca/english/information/applications/guides/5545E.asp In that case, you would have to contact the Canadian embassy to have them find out about that. If you knew when you got your PR, you could ask for a copy of this document but you don't even know that so it may be harder for them. You do however carry the risk that they will find your landing document and say voila, you were a PR but now you are not any more because you have not met the residency requirements and then it will not really help you. Unless you find your landing document in your parents things, there is no way of knowing that you are a PR without alerting immigration.
If they did send you a copy of your landing document without officially revoking your PR, if you get into Canada with that, you could live quietly for 2 years and then apply for a PR card which they would have to give you because you have made good on the residency requirements for your PR status. It would however be hard for you because most PR's do not show up in Canada with a 40 year old landing document. When you apply for a social insurance number, I do not know what they would do. Without a social insurance number, you would not be able to work and it would be hard to rent an apartment except in a room-mate situation. I also do not know if you would be able to sponsor your family during this time because then you are drawing attention to yourself again as living in Canada without meeting the residency requirements. That is, I think it is a very slim chance for that to work.
May I ask, why the sudden infatuation with Canada after 40 years?