The Simmons 2.5-7 Gold Medal red ring was a scope that could take the pounding of even "real" handcannons. Long discontinued, might come up used rarely. No other Simmons before or since can match that particular model.
Best of the best to handle the biggest handcannons by design... better than any name brand handgun scope is the Tasco Pro Class 30mm scopes in fixed and variable. Also long discontinued, but they come up for sale used far more often than the Simmons, and for hundreds less that what they cost new during their production run. A company in FL still services/refurbs them.
The early model Burris scopes stood up well to handcannons... later ones are iffy from what I've heard from others.
TC's scopes also got the job done for all but the heaviest hitters. No idea if their current models are as good as they were, but they'd be a strong choice.
Current made scopes you might consider - Burris, Leupold, Busnell or Nikon and hope for the best. I blew up a Leupold on a handcannon.
A 45-70 w/tamer is not as hard hitting as some others... but I'd want the TPC, Simmons GM, TC or an older Burris scope on it, and at least three rings (my harest hitters had 4).
FWIW-YMMV