I did communicate with an ATC operator at Toronto Centre, about this same question. The workload for these sectors, does vary. North Bay - High level is "Killaloe" 121.225 MHz, where the transmitter is located. The "Picton" transmitter is located in Coe Hill Ontario, on 124.675 MHz. And the southern sector of this so-called "trio" is the Barrie sector, above Peterborough, Ontario. That transmitter, for 134.575 MHz is at Pearson Airport (if I am not mistaken). Sometimes, all 3 sectors are "stand-alone", sometimes Killaloe will be stand-alone, and Picton/Barrie will cross-couple, or, Killaloe will cross-couple with Picton and Barrie is stand-alone. I used to live in North Bay, from 1997 to 2004 and listened to the Killaloe sector. The Killaloe sector, works with the Quebec sectors, such as the Ottawa Ontario NW region, the northern Laurentians, on 127.875 MHz, including the Sault-Ste-Marie High-Low sectors. Killaloe also co-ordinates flights, going in to Pearson Airport, Detroit, Chicago and much more.
I have seen the digital Communication box at the Timmins Flight Service. There is a row of settings for "Receive", "Transmit" as well as, Headset or Hand Mic. Timmins FSS has 3 positions, Timmins, Moosonee and Muskoka. The operators have access to all 3 airport profiles, on one screen. If they are working 2 position in one, for example, Timmins/Muskoka, they set up a "toggle" switch, to go back and fourth between the 2 sites.
The cross-coupling function, I forgot to ask how it works. It does take about 5 seconds to set it up. I did see an online posting for ATC cross-coupling, where a communications menu appears, and allows a "Transmit-receive frequency" to be enabled, onto the same button as another frequency. For example, if Killaloe wants to cross-couple with Picton, the controller would most likely press "Cross Couple", then select "Tx/Rx 121.225 on the 124.675" button, then press XC enable. And, repeat this same process for the "TxRx 124.675 onto 121.225.