Polearms, for the most part, use support weaponry.
Medium armor tends to be what you go for.
I personally use low level plate (Corazzina armor + Sugarloaf Helm) when going into most battles.
I've seen many successful polearm builds running around with cavalry robes, brigandines (upper level medium), and mail surcoats.
Canary himself cruises with lower tier armor (Khergit Lammelar) and looks damned sexy in it.
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HOWEVER
Polearms tend to be cheaper than two-handed swords, so you'll be alright with going with something more expensive as far as gear goes.