ssh does not transmit keystrokes, it transmits stream of bytes where a appears as a, 1 as 1, Ctrl+B as one byte we denote ^B, backspace may be ^H or ^?. Keys like F5, PgUp or arrows are transmitted as escape sequences. AFAIK there is no standard sequence for anything involving Pause/Break. You need to know what sequence (if any!) Windows is willing to interpret as Ctrl+Break, then set up your terminal emulator in Ubuntu to send this exact sequence upon Ctrl+Break. Your terminal emulator in your desktop environment may or may not be able to assign a sequence to the keystroke.