After the summit of Allison Pass, where Highway 3 crosses from the Fraser Valley Regional District into the Regional District of Okanagan-Similkameen, the road descends for 40 mi (64 km) along the Similkameen River before beginning another long climb up Sunday Summit (1,284 m (4,213 ft)).

Prior to the opening of Highway 97C in 1990, this was the primary link between the Lower Mainland and the Okanagan Valley, and still functions as the main alternative route.

Beyond the summit of Anarchist Mountain, in the upland rural community which shares the same name, Highway 3 enters the Regional District of Kootenay Boundary and proceeds to hug the Canada–United States border.

East from Christina Lake, Highway 3 travels for 47 km (29 mi) through Bonanza Pass to its junction with Highway 3B at Nancy Greene Provincial Park, which is the cutoff to Rossland and Trail, passing Red Mountain Resort en route.

[2] East of Burnt Flat, Highway 3 heads into the Selkirk Mountains and passes through the Kootenay Pass, at 1,774 m (5,820 ft) it is the highest point on the Crowsnest Highway, on a stretch known as the Kootenay Skyway, or Salmo-Creston Skyway.

In the early 20th century, the province began to upgrade its trails to roads, and in 1928, it was the first automobile route that connected to the Alberta border.

[3] Designated as the Southern Trans-Provincial Highway, it ran from Vancouver to Crowsnest Pass and later designated as Route 'A'; the route followed Kingsway and Yale Road from Vancouver to Hope, then turning north to Spences Bridge.

The route included major ferry crossings at Castlegar, Nelson, and Balfour, before continuing through Creston and Cranbrook to the Alberta border.

In 1965, the Rossland-Sheep Lake Highway was completed,[10] linking to the new Christina Lake-Castlegar section through Bonanza Pass (opened in 1962 with the completion of the Paulson Bridge),[11] replacing a gravel mountain road that had connected Cascade City and Rossland.

MOTI, the replacement road was built a relatively short period of thirteen days.

[16] The highway built immediately after the slide has now been bypassed by a new four lane alignment to the south, which opened in 1982.

Officials projected that Highway 3 would be the first of several damaged routes to reopen, and thus be the first to reconnect Canada's road network to Metro Vancouver.