sauanders makes several easels, two of which i have. their 14x17 easel is really an 11x14 one. in that that's the largest paper size it'll accomodate.
they also offer a so-called V track model, the advantages of which i can't attest to, but it's a lot more expensive. the universal 4 blade model is excellent. my only regret is not buying a 16x20 model so that i could use that paper size, but, using the 4 blades, crop to a smaller dimensioned image for mounting with 'corners' rather than dry-mounting. good luck!