I created a new ubuntu 14.04.3 VM and from the install screen itself I could not connect to the VNC Remote. I tried different browsers and machines with no luck. I tried different scaling methods in VNC Remote. Here is my XML:

<domain type='kvm' id='1'>
  <name>Ubuntu</name>
  <uuid>0976f710-c9cb-7320-9a86-bbd296ae03fb</uuid>
  <description>Ubuntu VM</description>
  <metadata>
    <vmtemplate name="Custom" icon="ubuntu.png" os="ubuntu"/>
  </metadata>
  <memory unit='KiB'>4194304</memory>
  <currentMemory unit='KiB'>4194304</currentMemory>
  <memoryBacking>
    <nosharepages/>
    <locked/>
  </memoryBacking>
  <vcpu placement='static'>4</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='0'/>
    <vcpupin vcpu='1' cpuset='1'/>
    <vcpupin vcpu='2' cpuset='2'/>
    <vcpupin vcpu='3' cpuset='3'/>
  </cputune>
  <resource>
    <partition>/machine</partition>
  </resource>
  <os>
    <type arch='x86_64' machine='pc-q35-2.3'>hvm</type>
  </os>
  <features>
    <acpi/>
    <apic/>
  </features>
  <cpu mode='host-passthrough'>
    <topology sockets='1' cores='4' threads='1'/>
  </cpu>
  <clock offset='utc'>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='hpet' present='no'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/qemu-system-x86_64</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <source file='/mnt/cache/VM_DATA/Ubuntu14/vdisk1.img'/>
      <backingStore/>
      <target dev='hdb' bus='virtio'/>
      <boot order='1'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x04' function='0x0'/>
    </disk>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <alias name='usb'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <alias name='usb'/>
      <master startport='0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x02' function='0x0' multifunction='on'/>
    </controller>
    <controller type='sata' index='0'>
      <alias name='ide'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1f' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pcie-root'>
      <alias name='pcie.0'/>
    </controller>
    <controller type='pci' index='1' model='dmi-to-pci-bridge'>
      <alias name='pci.1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x1e' function='0x0'/>
    </controller>
    <controller type='pci' index='2' model='pci-bridge'>
      <alias name='pci.2'/>
      <address type='pci' domain='0x0000' bus='0x01' slot='0x01' function='0x0'/>
    </controller>
    <controller type='virtio-serial' index='0'>
      <alias name='virtio-serial0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x03' function='0x0'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:46:b6:df'/>
      <source bridge='br0'/>
      <target dev='vnet0'/>
      <model type='virtio'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/>
    </interface>
    <serial type='pty'>
      <source path='/dev/pts/0'/>
      <target port='0'/>
      <alias name='serial0'/>
    </serial>
    <console type='pty' tty='/dev/pts/0'>
      <source path='/dev/pts/0'/>
      <target type='serial' port='0'/>
      <alias name='serial0'/>
    </console>
    <channel type='unix'>
      <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/Ubuntu.org.qemu.guest_agent.0'/>
      <target type='virtio' name='org.qemu.guest_agent.0' state='disconnected'/>
      <alias name='channel0'/>
      <address type='virtio-serial' controller='0' bus='0' port='1'/>
    </channel>
    <input type='tablet' bus='usb'>
      <alias name='input0'/>
    </input>
    <input type='mouse' bus='ps2'/>
    <input type='keyboard' bus='ps2'/>
    <graphics type='vnc' port='5900' autoport='yes' websocket='5700' listen='0.0.0.0' keymap='en-us'>
      <listen type='address' address='0.0.0.0'/>
    </graphics>
    <video>
      <model type='vmvga' vram='16384' heads='1'/>
      <alias name='video0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <alias name='balloon0'/>
      <address type='pci' domain='0x0000' bus='0x02' slot='0x05' function='0x0'/>
    </memballoon>
  </devices>
</domain>

I solved it!!!

When I 'Force Stop' the VM and 'Start' it again, then I am able to connect and see the desktop fine. Even if I restart the VM I could not connect. Its strange!

Once I connected I changed the resolution (which was set to some crazy high resolution) to 1920x1080. After that I don't have any issues so far!

 

In addition I also changed the machine from pc-q35-2.3 to pc-i440fx-1.4. Not sure which is better type for Linux guest OS.