The real question is the provenance. As mentioned above, it would be easy to put one together and not an unlikely combination, especially in the 20s or 30s, for someone in Canada who wanted a scoped hunting rifle on a budget.
Find out as much as you can from the little old lady and research the military service if any, of the family member(s) she says it belonged to, or whoever it did belong to, if that is known.
A number of Canadian battalions in France put together their own rifles with Win. A5 scopes. Whether they were marked in any way is not known AFAIK, but probably they bought them directly from the USA and so they would not likely have any War Department marks as they would not have gone through the usual inspection and acceptance channels.
If the rifle can be authenticated as a WWI bring-back it is worth whatever someone is willing to pay and these days the 3-5K $ mentioned would be no problem at all.