Depending on the fermentable portion of the sugars in the guava, I would lean towards doing a secondary fermentation on a bed of the fruit. That way you have more chance of getting some flavour into the beer.
Maybe split your weizen, do half on a bed of guava, the other half leave as is and sample side by side?
(My second AG will be a split rasberry weizen similar to above, making it in a couple of weeks...)