Looking to upgrade Galaxy S3 to an Android with a big display for ~ 350usd MAX, Need help!

As the title simply states, I am looking for a 5.5" + display (preferably 6") unlocked android phone to replace my aged samsung galaxy s3, I am hoping to get good battery life, an improved camera performance, nice display, and overall have something new and unique in general. I have been extensively searching the last 2 days but still cannot come to a conclusion. Lately I have primarily been looking at the NEXUS 6, Huawei mate 7 or even the mate 2 which I have read is a good bang for the buck.. but is it a bigger upgrade from the galaxy s3 was the question I had.

Anyways... If anybody can give me their thoughts or perhaps know another good phone with the qualities I am looking for, please feel free to chime in.

PS. I am a Canadian resident looking to purchase an unlocked phone in the US for price and selection reasons.