My PAL/RPAL course instructor was retired police officer. His suggestion to us was that we make a point of always carrying our PAL and registration certs with us when transporting or using firearms. It's one more way of making sure that we're less likely to be inconvenienced by ignorance. Even if it's not a legal requirement, it is one extra layer of insurance against a police officer that is having a crappy day and has been misinformed about Canadian gun laws. Never assume that someone else is informed, and never expect the benefit of the doubt.
I personally tend to ensure that I have the appropriate documents with me by keeping my PAL in my wallet, and copies of my LTATT and all reg certs in a package that I put in my range bag when I'm transporting any firearm.
Given the prevalence of ignorance and misinformation about firearms and firearms laws here in Canada, every chance you get to be a positive example of gun ownership is worth something to us. Go ahead and mention that you aren't required by law to provide the registration on a non-restricted firearm, but also state that you happen to have it with you and have no objection to showing it the constable.