Do you know if Dennison could be a Danish name?!
Answers: I am wondering if Dennison were anglicized from Danish what could the Danish name be?
Danish ... not likely. Danish (and Norwegian) names use a -sen ending. Swedish names use a -(s)son ending, which has been Anglicized to just -son.
Dennisson would mean "Son of Dennis," and Dennis is, most definitly, not a Scandinavian name -- its actually French. Which means either; 1) it is a French Norman name that became transplanted in England after 1066, or 2) It was simply a creation of the English amalgum society in the Early-modern era (or after).
Most Scandinavian last names are just extensions of ubiquitous first names, such as; Per, Ramus, Magnus, Anders, Johan, et al. Accordingly, the corresponding last names would be; Persen, Rasmussen, Magnussen, Andersen, Johansen, et al.
Scandinavian culture permiated Northern English and Scottish society -- most of those areas were actually Norse settlements (and a part of the Danish Kingdom for over a hundred years prior to William the Conqueror). Hence, as England evolved those Norse Englishmen influenced their societies. 'Johan' became 'John,' and the Norse tradition of assigning afternames denoting one's father changed from 'Johansen' to 'Johnson.' This practice of giving afternames with -son on the end eventually became widely adopted by non-ethnic Scandinavian in England (i.e. Richardson, Thomason, Davidson, etc ...). As was stated before the French Normans (also Scandinavian in descent) influenced English culture, and brought with them Franco-Norse names ... one of which was most likely Dennison.