I'm assuming you are wanting to use guava paste and not fresh fruit. The paste will give you more of the flavors I think most people associate with guava. You might want to consider something with a little "funk". Try researching a lambic recipe and work it in that way. But again assuming you are using the paste I would make sure you cook it in some water to loosen it up into a thinner paste instead of big ol' hunks of jelly that will take forever to break down in your kettle of fermentor.
Or you could do a Saison like Cigar City Brewing has done. I've yet to try it but here's a link. It looks like they use a secondary and add the beer to the puree.
You could possibly use a product like this http://www.amazon.com/Culinary-Tradi...5959416&sr=8-1
but it would be a bit pricier than using guava paste.