1. Your parcel was sent back to China possibly because Canadian Customs did not authorize the parcel in Canada. Or maybe it could not be deliver with the address that was mark on the parcel. Why it took only 3 days to arrive in Beijing, possibly there was enough room on an Aircraft flight for the Mail Bag with your parcel in it to depart Canada for China.

2. Why it took so long from China to Canada, Canadian Customs Office in Vancouver are the culprit. Normally it takes 5 to 6 weeks before delivery when it goes through Vancouver Inbound mail.

3. Quote:
my package is "2016-07-09 13:37:45.0 Beijing Transit Station import customs cleared (domestic transit )"
Unquote
Means that the parcel is importing from another country, in this case from Canada. The parcel will be eventually be sent to the sender of the parcel.

4. You should contact seller and tell him the parcel is returning to him and you don't know why.

Hope this help.

1. Quote
I'm wondering what is the your policy if the seller is no long at his location and you are unable to deliver the package back to him. is there anyway to have the package resent to me in that case?
Unquote

2. If a parcel can not be deliver to sender address on the parcel then it will be kept by China Post. If seller want the parcel he need to call China Post Hot Line: 11185 and either arrange for a new delivery or pick up the parcel.
I suspect after a while with no news of the seller parcels are destroy.

3. Parcel will never go back to you in case of non delivery to the sender because it was refuse entry to Canada or the parcel was not deliverable.
If seller did not put the right address (postal code missing, street number missing etc) then Canada Post just put non deliverable parcel and return it to sender.

4 When seller receive the parcel he should be able to tell you what happen to it. There should be indication on the parcel.

5. Quote
I will contacting Canada Customs tomorrow to find out why my package was rejected as I doubt the address is an issue as I have been living at the same address for a number of years now and have had other packages from china delivered here with out any issues.
Unquote

I doubt that Canada Customs Office will be able to tell you something on your parcel. May be the best person for that answer will be Canada Post because they are the one scanning the parcel. In their system they might be able to know what happen. If you are close to a Post Office, just ask to see the supervisor and explain to him your situation and could he look into the system if he knows the reason why it was sent back to China.

Hope this help.

1. This is the full tracking of your parcel:
Parcel No.RM698377033CN tracking result
2016-05-29 17:16:08.0 南阳city 大宗parcel 集中shipping center received
2016-05-29 18:15:10.0 南阳city 大宗parcel 集中shipping center customs scan
2016-05-29 18:31:09.0 leaving 南阳city 大宗parcel 集中shipping center ，next station 南阳center
2016-05-30 10:49:26.0 郑州Transit Station export security scan
2016-05-30 10:55:32.0 郑州Transit Station export customs cleared
2016-05-31 03:34:00.0 arrive 郑州Airport
2016-05-31 15:22:02.0 leaving 郑州Airport going to next airport/seaport
2016-06-02 08:35:00.0 郑州international departure
2016-07-06 09:13:00.0 Vancouver export customs cleared
2016-07-09 09:52:37.0 Beijing Transit Station import customs scan
2016-07-09 13:37:45.0 Beijing Transit Station import customs cleared (domestic transit )
2016-07-12 09:28:11.0 郑州Transit Station import customs scan
2016-07-12 13:41:17.0 郑州Transit Station import customs cleared (domestic transit )

2. Last tracking on an other site is this:
2016-07-12 13:41
Zhengzhou Exchange Bureau, import each other (internal transit)

3. Parcel is still in transit but I guess close to him now maybe a few days away. You can track it here:
http://www.track-chinapost.com/track.php?code=RM698377033CN&fc=0

Hope this help.