Generally, itís better to remove the siding at the point where your deck plate will be attaching to the house, then fabricate some flashing over the deck plate which goes under the siding above what you removed. With a couple of exceptions, thatís the way I have done it.
I know, aluminum siding is not easy to cut. I once saw a deck builder simply flatten out the bottom siding panel with a hammer, then simply bolt on the new deck plate on the outside. Well, it distorted the subsequent panels above the flattened piece.
You can get a metal saw blade for your circular saw, which will do a pretty nice job of cutting it, or you can remove the sections and use metal shears. Or, or, you can build a platform below the siding, if enough of your basement/foundation wall shows (if you have one). On one project, the deck was only a foot off the ground, so I used those pre-made concrete piers and did not even attach the deck to the house, avoiding any cutting of the siding at all.