I've used one 6x4 photo here with two 3x4's either side. I use photoshop to put to 3x4's on a 6x4 canvas for printing but with the popularity of Project Life style scrapbooking there are a lot of apps around which will allow you to easily to the same. If you're already using one perhaps you could share it in the comments and let us know if it is for Apple, Android or both?
The base of this page is Cocoa Vanilla ~ Wild at Heart Artisan- I haven't done a thing to alter it... that beautiful water colour effect and the little crosses are part of the design. It's so lovely I plan on getting a few more sheets for my personal stash.