That has been an embankment for well over 100 years - I've seen photos that proclaimed that they were from the 1880s of the area, and there is no sign of any trestles through there. Any trestle that did previously exist has since become part of the embankment.
Dan, I've searched extensively for any photographs before the 1920s, and I'd be very interested in seeing what you've seen! As far as I know, the last major work on that embankment was in 1926 (see picture below, looking east from the southwest side of the Smalls Creek).
For the record, the same technique was used to raise the tracks into Union Station from the east - that was done in the 1920s, and there is no sign of any of the wood from that construction.
There's a good photographic record of that work - as far as I can tell, that work was done about the same time as these photos were taken. From around Pape to Union they appear to have built a trestle explicitly for building the embankment, dropping the soil from railcars, to fill the embankment. (which makes me wonder how good the compaction is).
I'm surprised there'd be no trace left of the wood after about 100 years. I've done drilling before downtown south of Front Street, and hit large pieces of timber, which must have been of a similar age, and below the water table. I'd think the old trestle, mostly above the water table, would be better preserved.
The Grand Trunk began double tracking the Toronto-Montreal line in 1887. Perhaps that's why and when any trestles were filled in.
Ah, that's interesting - perhaps related to Dan's 1880s photos. Yes, it could have been done then. Though that's an awful lot of soil from that early - though it's just about the time of the advent of steam shovels - I'm not sure when they started to be used locally.
Metrolinx' response to the community over Smalls Creek was downright shabby, but I don't see reverting to a trestle as technically feasible today.
I spoke to some railway engineers (not that type of engineer!), and I was pointed to some work in the USA recently, where after a trestle failure, an embankment was quickly built through a floodplain, when was then replaced by a trestle without further interrupting traffic on the railway. Not as easy as building one without rail traffic - but quite doable.
What do you see as the constraint - other than cost?