Make a montage with the two tracks in it and fade one in as the other fades out. simple.
Watch the master output though as the cross fade may peak the mix. If it is a very small quick peak then use a limiter at 0dB if it is more substantial then lower your waves volumes or change the fade in/out settings.
remember to add markers at the desiered point ot break up the two tracks, but when burning the CD with wavelab make sure in your basic audio project that there is no pause gap between tracks. (its usually set to 2seconds)