Hmmmm..... Wonder what you consider giants.
All the Miscanthus sinensis cultivars will do well for you in zone 5. Some of the bigger ones include Roland & Goliath
Miscanthus floridus (aka gigantius) should also do well for you - it is certainly one of the biggist grasses out there.
Saccharinum ravennae (aka Erianthus ravenae) is also quite tall however, not as vigorous in zone 5 as it it further south.
Arundo donax is another tall one that should do well for you.

Containers?? Well, aside from the considerations of the container surviving the winter .....
I have had luck with Miscanthus purpurescens, Calamagrostis brachytricha & Elymus arenarius overwintering in large half whiskey barrels. Unfortunately, none of these are giants ....
A.

How about Arundo (giant reed). I have grown it in zone 4 for over 15 years and it just gets bigger and taller each year! Just mulch it good in the Fall after cutting the canes off. Mine grows to at least 15-18 feet tall.

Thanks for the suggestions

Have you checked out the bluestem nursery in BC? Lots of different varieties.
flora2b

Here is a link that might be useful: bluestem nursery