If you can butt the factory edges together it will make a pretty clean seam, but you can make a nice straight cut with a razor knife and a straight edge. If you overlap the two pieces and cut through both they should line up nicely. Glue it down and come back later and seal seam with black silicone and the seam won't be noticeable. Just don't make your seam where sub flooring is seamed.
I haven't used AdvanTech flooring but I can't see an advantage to using Luan. You're not going to use the Advantech somewhere else later are you? Keep it simple, less layers is more better.
Curious though, why didn't you just get a 14' length and only make 1 cut down the side and no seam? There may be a little more scrap but no seam. .....

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McDave
Edit; I just looked at the link, I guess you should use grey silicone to seal seam. Great price @ .50/sq,ft. ...

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McDave