You must be prepared for wet weather as Alaska gets a huge amount of rain but the sun does shine as well. In april you can expect to have some warm weather but there will be times when it gets quite cold so layers of clothing would be best. It can get quite cold on the Pass and also whale-watching so waterproofs, sweaters, sweat shirts and long sleeved shirts would be preferable and if you have them take some walking boots as they will prove useful in the towns and on tours. regards Nei.
Good choice,my wife and I went in april 2004 and in Vancouver we were happy in TEESHIRTS!For the cruise take a woolly jumper,stout shoes,fleece/body warmer,waterproof anorak type top coat.
Remember if warm you can always strip off a layer or two!! ps. remember to do the white pass and yukon railway tour,the scenery is out of this world. enjoy.