Your area behind the brick should have a drainage plane to give moisture and water build up an avenue of escape but you dont want physical water getting behind it in large amounts, so you need to flash the transition point. We went with copper on all our flashings. It's pricy but warranted in our location. It was an astetic choice as well as we have many flashing areas exposed on the roof lines with valleys, wall to roof connects, etc. I'd be concernrd with aluminum if your are coastal with salt air. Galvanized or galvalume is fairly common in most areas.

Your top course of the brick looks like it is sitting level. The only time I sided up to a brick wainscot similar to yours, the top course was sitting at a 5 degree angle. We had flashing made up at a sheetmetal shop , If I remember correctly, 3" x 3" with a 5 degree bend to slope with the top course. We used a bitumen type caulk for maosnry/metal and ran that bead under the front lip where the flashing met the brick tucked back far enough to where you couldn't see the caulking just to prevent big water intrusions from making it's way back in under the flashing back to the wall.

Aluminum should not be in constant contact with water or a water retaining material like brick because it has little resistance to galvanic action. It has additional problems with cement mortar. It is only appropriate for flashing when the exposure is small and drainage is good. Special coatings may allow it to last longer but they increase the cost.

In this case you need to slope the top course as much as possible (or install a cast stone or copper coping) and install flashing below that course to limit the amount of water that gets into the cavity (unless the flashing at the floor line is adequate for that purpose). Such a short brick wall can't follow any conventional flashing solution.

A minimum treatment would be copper "L" flashing starting under the house wrap and sitting on the top brick course projecting as far out and down as you can afford. There would a direct trade off between the amount of exposed copper and the steepness of the slope.

I suppose you could also consider an oversized "watertable" sitting on the top of the brick as if this was a wood framed structure sitting on a brick foundation but perhaps the windows would look strange.

It's a tough detailing problem. Historically brick usually stops at the bottom of floor framing to avoid these issues.

Following what Renovator8 suggested, the only stormproof flashing is going to be a custom-shaped copper drip cap that extends to and over the edge of the brick coping. Anything less is going to be relying 100% on caulk for the seal. If the brick is in fact level on top as has been suggested.
If this were traditional shake siding, I'd recommend flaring the shakes out so they cover the brick, but this can't be done with your panelized shake system.
Casey

I've successfully used cast stone atop a first floor brick wall with board and batten above, flashed with aluminum as per the manufacturer's directions. I've also seen concrete pre-cast copings used the same way.

While brick roll-offs under windows are susceptible to damage, it can take decades for the joints to deteriorate, even in cold climates.

It's time to talk to your building code inspector.

Under the International Residential Codes from 2000 to and including 2012 version, flashing should have already been installed under the weatherbarrier (housewrap) and over the top course of brick and under the rowlock...with weep holes installed under the rowlock on top of the flashing.

So what you have in place is already done wrong.

See Page 9 of the PDF link below for details.

That said, and after having the IRC in effect for nearly 8 years in my state, proper code compliant brick installation and flashing detail still escapes most masons, brick installers, and contractors.

"Been doing it this way for 30 years" we always hear.

As building inspectors, we reply..."Well you've been doing it WRONG for 30 years."

Here is a link that might be useful: Guide To Inspecting Residential Brick Veneer

Not sure if it makes a difference but, the brick wall stops about two inches below the first floor framing. The brick also is a few inches off the stem wall with weep holes at the bottom of it.

Our flashimg extends to the end of the brick. Do we paint it?