Susan, I have the 1850 census for your Sam and Sydney McClennen from Philadelphia. My family name is McClenin, but I collect just about anything I can that is close to the spelling. My gggrandfather John McClenin was born somewhere in PA about 1817. He appears in a NY city directory in 1850 and then in the 1860 census in Poughkeepsie, NY where he dies in 1864. He married a Katherine Maloney from Canada - you mention Canada as a possible connection to your family. I do not have any info on John's parents.
Hope you have progressed in your research since 2002. I am really stuck with my McClenin family. Would love to hear what you have found.Jean Driscoll