Having a long wav file imported into reason whole and then trying to match the beat is very hard, especially when you havent set the right hit point on the pella.
The hit point being the start of the verse, so you can match the beat to it.
The best way would be to get a copy of the original song, then tap out the rythm to it using the tool posted above. This isnt always fool proof, as pellas tempos can be different from the original, depending on how it was recorded to wav. Listening to the original is the best way to hear how it should sound, before you try remixing it.
If you are going to use just reason and not rewire, then I suggest you chop the pella into smaller peices say...
intro,
verse,
hook,
verse,
hook,
verse etc.
smaller peices are easier to get the timing right with.
trying to acheive what you are doing in reason can be awkward..