Not with the same miles, you can't. US Airways has moved from Star Alliance (with United and Air Canada) to oneworld alliance (with AA and BA). And the US Airways FFP will be disappearing in a months (being merged into the AA AAdvantage FFP).

Credit your BA flight(s) to US Airways.

Credit your Emirates flight(s) to JetBlue.

Credit your Air Canada flights to United.

But you won't be able to combine those three together unfortunately (either at the credit stage or at the redemption stage). That's the downside of booking a flight with so many different carriers without paying attention to alliances at booking time.

However, once US Airways merges with AA, they'll allow one-way awards, as United already does. So you could book one direction to Hawaii on AA and the other direction on United, assuming you have enough miles for one direction on each of those (but not enough miles for round trip on either).