No idea on validity of the the cancel but there was a post office in Cecil County Maryland called the "Brick Meeting House" as per the Table of Post Offices in the United States as of Oct 1. 1846. Hobsun
The cancel looks to be the correct shape and arrangement, but it also seems to be way too fresh to be from the period. It is easy to forge cancels with modern scanners and computers and 3-D printing and such if one has a original to scan. Of course, it could be real, but I would not buy it if it were offered to me.