I have the same problem. Doesn't matter whether T3 Cap Gains Box 21 is entered with EasyStep or forms, it does NOT show up on Schedule 3 at all.
TurboTax help is terrible. There isn't any information on what appears to be new Boxes for T3 Box 52 and 53 (never seen them before) AND there seems to be inconsistency in terms used for Boxes 25/34. Tax slips still call it 'Foreign non-business Income' and 'Foreign non-business income tax paid'. EasyStep AND T slip entry/Forms method don't use the same terms this year.
