There is only one file type that uses the .U11 extension:
UFile 2011 Tax Return
Canadian tax return created with UFile 2011, a tax preparation program for Canada residents; contains federal Canada tax forms and the associated data entered by the user; may be printed and mailed or filed electronically using the program's NETFILE feature.
Data from a U11 file can be opened directly by UFile or imported by the Canadian version of TurboTax.
Updated: May 26, 2013