Let me throw something out there and in this respect I do not know what the present arrangement for the Latvian eFB BG nor the artillery support it gets currently but let's do a hypothetical.
In short, Latvia has one mechanized brigade (without tanks) and four National Guard brigades (essentially light infantry).
The eFP BG is a heavy BG with four mech coys (two of which have their own integral tanks platoons) and a further armoured company. It also has a mortar platoon but no integral artillery (notwithstanding the four M777s just sent over.)
Latvia does now have enough M109A5OS to form three x 18-gun battalions; which is interesting.
Lets just play with numbers.
If one were to add that brigade HQ and those four tank squadrons and two LAV companies that you recommend then you could clearly form two combined arms battalions which, together with the eFP BG (also a combined arms battalion) would give you the manoeuvre elements of an American ABCT (notwithstanding the issue of the LAV as an IFV - you play with what you've got).
If Latvia/Multinational Division North would then put one Latvian M109 battalion in direct support of that brigade then all that would be needed to complete it is a cavalry regiment, a CER, a Svc Bn and some SHORAD. (Some if not most, of the cavalry elements could come from the overly strong eFP BG - it would need some rejigging) You could even send those M777s home or assign them to work with the light Latvian National Guard brigades which would suit their role better.
Another benefit of getting a commitment of an M109A5OS battalion assigned by Latvia would allow 1 RCHA's M777s to be redistributed to up gun 2 RCHA and 5 RALC. 1 RCHA could be reduced to a brigade FSCC, An OP Bty with three tactical groups (a BG FSCC and three FOO/JTACs), an STA battery and a small gun battery with C3 howitzers to provide live fire trg support to the FOOs.
Whether there is a need or not to deploy more elements to Latvia (other than the obvious maintainers and log/admin staff to keep the prepositioned equipment maintained, is an open question. My personal preference is to keep the rest of the force in Canada but flyover frequently to exercise the equipment, the personnel and the plan.
What is necessary is to ensure that 1 CMBG maintains enough tanks and LAVs to train itself throughout the year as well as a brigade's worth of reservists as augmentees/replacements. That would entail stripping 2 CMBG of at least one LAV bn (I would prefer both and sending the second to 5 CMBG thus making 2 CMBG a light brigade) 2 CMBG would therefore be relieved of the Latvia rotation role and look at other missions while 5 CMBG would still take part in eFP BG rotations but not the flyover role.
That really only leaves one major question. Are there enough tanks left in Canada to train the LdSH as well as at the CTC (and should those functions be combined in Edmonton?) One solution might be to reduce the number of tank squadrons in Latvia to three and increase the LAV companies to three. That would make the forward deployed brigade slightly tank lighter than an ABCT but still viable. Another is to pick up another squadron of Leos - there are still some in storage around Europe.