In Phnom Penh, how much roughly should we expect to pay for driver and guide for 2 days sightseeing to main sightseeing spots. Also is it the same for SIem Reap.
With tuk tuks it is often not how long you hire them but how far you want to travel in them. Going some way out of town can add to your costs.
I think I paid about US$12 in PP and US$15 in SR. You can ask the owner of the place you stay in and most will give a good figure for the day out. The tuk tuk driver will of course want more.
In Phnom Penh, that was the Genocide Museum, the Killing Fields exhibit outside town, the history museum in town and some other places.
In Siem Reap, that was Angkor Wat and all the small temple sites close by, but beyond walking distance. The driver did mention another one some distance away but that was more and I was all templed out by that time.

Slightly more in Siem Reap than Phnom Penh.
You can probably see all the sites in Phnom Penh that are not central in one day.
Guides have increased their fees quite a lot the last 12 months (supply and demand). Expect to pay USD 40.00 up (depending on language); more if you want to do sunrise/sunset as well. USD 15.00 - 18.00 for a Tuk-tuk. These prices are for SR.

recently 12-15 for angkor wat and angkor thom by tuk tuk.with sun rise or sunset add 3-5

Last year at Angkor tuk-tuk was $15/day for normal days, $30/day for outlying temples, sunrise and Tonle Sap days. Seemed to be quite standard. Cold water in icefilled cooler box was included in the price.

Hi - we have just come back from a trip including Siem Reap and Phnom Pehn. We paid $13 for a day in Siem Reap for the 'inner temples', $15 for the 'outer temples', $27 to go to Banteay Srie and Kebal Spean - water was available on the tuk-tuk each day. We paid an extra $3 for sunset and $5 for sunrise (or might have been the other way round).
In Phnom Pehn, the place we stayed at had a list of suggested prices that the tuk-tuk drivers stuck to like glue. We paid $15 to go to the Killing Fields and museum. Trips around the centre tended to be $2-3. Interestingly we were in the tuk-tuk with 2 Cambodian women who were being dropped off at the Central Market (long story) - they paid 1,000 Riel where the cost to us was $2!
In Siem Reap the tuk-tuk was arranged through our guesthouse and was great
Have a great trip