Lack of photographic evidence certainly does not mean there was no bridge.
No, but when it doesn't show up in pre-Hazel aerial shots, the idea it was destroyed by the hurricane and never replaced is put to bed. I've found old maps to be wholly unreliable. They predict roads that were never built and lay them out as though they existed, they play fast and loose with the actual course of any road that isn't a straight line, and they famously propose bridges that were simply on county wish-lists. I have a map of Toronto from 1955 that insists a bridge connects Woodvine Ave. to Woodbine Heights. I've been there to check it out and the idea is plainly absurd; even now it would be an engineering headache, and a useless one since Woodbine Heights leads nowhere beyond.
The same is true for Humberline. It was close enough to Hwy 27 that, while York County might have intended to bridge it eventually, there simply wasn't the pressing need to, and I don't imagine it ever got off the back-burner, unless the local farmers did it. If so, no doubt the Humber flooded anything ad hoc away enough that they eventually would have just given up. But I know all kinds of obvious places for bridges that never were, or weren't until the need and money met in the middle. Steeles itself didn't even cross the Humber till 1983 (though I've seen older maps that insist it did -- again, wishing in advance of doing), so it's hardly remarkable that a road like Humberline never did. In Mississauga, Eglinton didn't cross the Credit till the end of the 1960s, and Burhamthorpe until 1973, I believe. Sheppard still doesn't cross the Humber, though a direct conncection to Rexdale would be of real use (not infrequently to me). There's never been a bridge completing Post Road, either, though again I've seen maps that suggest one was there.
I don't know if it's your bailey bridge, but the point is, when a bridge exists (esp. predating Hazel) in Toronto, there's always photographic evidence of it, if only from above. Re: Indian Line...
And as I've said, in the 1953 aerial image of the region, there's no bridge at Humberline over the river. This was a pet project of mine, too, before I ever saw it mentioned here. If there was every anything there, there's no hint of it now, and it was never anything substantial.