The way I read your diagram (apparently incorrectly), is that SW2 is a 120v switch (has H1 and N poles), that controls the coil of a double pole, single throw, normally open, 240v, 30a, mechanical contactor (SW3). That allows you to switch the element off regardless of what the SSR is doing, a good safety feature because SSRs can fail closed (on) and they leak voltage.
But given what you have said, SW2 is a single pole, double throw, 30a switch that enables you to switch between H1 and N, making your element switchable between 120v and 240v. SW3 is a double pole, single throw switch that allows you to switch the element off as I described above.
That said, I like my misinterpretation better.
You would always run your element at 240v and use the PID manual mode to control the boil. That gives you to set the PID to cycle the element anywhere from 0% to 100%, and will give you much more control than than switching from 120v to 240v, which effectively gives you 0%, 25%, and 100% options. That might work for you, but what if you needed 70% to maintain the boil?
I would put the SSR inside the box with its attached heatsink outside the box.
Perhaps some our northern brethren could point you toward some purchasing options in Canada.
P.S. In my configuration you could also just go with SW3 (double pole, single throw, 30a switch), rather than a separate switch (SW2) with a mechanical contactor.