I see this fight ending somewhat similar to the Wlad-Brock fight. Walcott was very crafty, and tricky defensively. He also would be outweighed by 50 pounds or so. He could hit pretty hard - for a cruiserweight. Wlad would have the advantage in every single physical attribute (maybe except for chin). I see Walcott frustrating Wlad early with angles and movement, but eventually getting overwhelmed in the middle rounds by the much bigger, faster, and stronger Klitschko. Not that Brock is anywhere near Walcott's overall talent level of course. But, his big size advantage over Walcott would make them fairly close to each other, at least in terms of being a challenge to Wlad. And the way Brock was able to frustrate Wlad early would be similar. The other scenario is that Wlad jumps on Walcott and overpowers him in one round, ala Marciano, but I know there would be plenty of people flaming me for being too much of a Wlad fan, or not respectful enough to the old timers, etc.
Walcott could really cause Wladimir a lot of problems, but if Wladimir is able to control the distance and use his jab effectively, the right hand should land eventually. Wlad by decision or late round stoppage.