I use mythtv with Rogers, so I can tell you that what you want to do is well supported by myth/linux.
You mention you have a PVR-500, but do you have an IR-blaster? I use the MCE remote with the blaster to control two SD STBs from Rogers (SA E940 and SA 3200). They're connected via S-Video to a PVR150 and PVR250.
In the settings I enabled "Power On with numbers". This generally works well. After a power outage, I do have to verify that the boxes came up OK, because they don't always.
I use mythbuntu, and its Mythbuntu Control Centre, which allows configuration of many Mythtv and related settings, including lirc, remote types and set top box codes. There you can select the appropriate remote, and blaster, and STB codes to transmit. Even if you don't use mythbuntu and the Mythbuntu Control Centre, I think the install of lircd asks what remote and transmitter codes you want to use.
The SA transmitter codes are found at the following location on my system.
I use this channel change script. I'm sure you can find versions of it around
irsend SET_TRANSMITTERS 1 #1 is on the left when looking at the front of IR receiver, 2 is the other one
for digit in $(echo $1 | sed -e 's/./& /g'); do
irsend --device=/dev/lircd SEND_ONCE $REMOTE_NAME $digit
sleep 0.4 # note, you may have to tweak the interdigit delay up a bit
irsend --device=/dev/lircd SEND_ONCE $REMOTE_NAME SELECT
There's something similar at the mythtv wiki.
For the HD STB, there's the additional option of using firewire to change the channels. I use this to control a 3250 and 8300HD.
There's some sample code here. http://www.mythtv.org/wiki/Sa3250ch
I had to make some modifications to recognize the 8300hd.
Using firewire also allows you to query the power status of the box, and turn it on if necessary using stb-command. http://www.mythtv.org/wiki/Stb-command
Using a script, you could query the power status, turn on the box if required, change the channel, and then add a delay before the HDPVR starts to record.
The delay is important to prevent messed up recordings, or recordings with no audio on the Hauppauge HDPVR.
The only other issue I've run into is the automatic power off of the 8300HD 1:10 AM. To avoid this issue I have a cron job an send exit command at 1:10, 3:10 and 5:10 via the IR blaster. I think this may not be a problem anymore, but the cron job's still running, just in case.