Since Ridley Scott was intimately involved in the Dune Film before, during and after the making of Alien. Has Ridley Scott ever been asked if the Alien franchise is canonically connected to Frank Herbert's Dune in a filmed interview?
There appears to be no in-universe connection between Dune and the Alien universe although both (briefly) shared a film director in the late 1970s and H.R. Giger worked on both projects as a concept artist.
Ridley Scott was asked to direct Dune and was actively involved in the project during the late 1970s, including having multiple meetings with Frank Herbert but ultimately left the project after his brother died of cancer. He'd already passed on Blade Runner but picked it up after a rewrite.
I was attracted to Dune because it was beyond what I had done on Alien, which was a hardcore horror film. Dune would be a step strongly, very very strongly, toward Star Wars.
You may also wish to note that the two universes are technologically incompatible. FTL transit in the Alien universe is accomplished by the use of hyperspace/subspace and is a mature technology that is essentially foolproof. By comparison, early faster-than-light transit in the Dune universe is described as being deeply unsafe, requiring the use of psychic "navigators" to remove the inherent risk of ploughing into objects. Travel in the Alien universe is very fast (thousands of times the speed of light), but travel in the Dune universe is near-instantaneous, resulting in the translation of ships from one point in space to another in milliseconds.