Yours looks the same as mine SG9 so boot space should be identical. Haven't tried to get a specific boot liner. I just use a bit or tarp as I don't have any animals to transport.
In terms of tonneau cover do you mean the pull out cover that fits behind the seats and covers the boot?
If so mine came with the standard Scooby one and it should be the same as any SG forester (doesn't need to be STI)
No idea on the dog guard I'm afraid
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